Metal production by electrolysis



METAL PRODUCTION BY ELECTROLYSIS No Drawing. Application November 19, 1952,

Serial No. 321,445

6 Claims. (Cl. 204-64) This invention deals with a process of producing actinide metals by electrolysis, and more particularly with .their production by electrolysis of fused actinide halides.

Actinide elements have been prepared heretofore by electrolyzing melted halides admixed with fused alkali metal halide and/ or alkaline earth metal halide. In these previously used processes bath temperatures of at least 500 C., but mostly. of approximately 800 C., were maintained during electrolysis. In the case of uranium production, for instance, these processes resulted in a fine powdery material which was very pyrophoric and had an undesirably high content of impurities, especially a high carbon content.

It is an object of this invention to provide a process of preparing actinide metal which has a high degree of purity and in particular a low carbon content.

It is anotherobject of this invention to provide a process of producing actinide metal of high purity from technical grade materials.

It is still another object of this invention to provide a process of producing uranium in a coarse crystalline form which is relatively little pyrophoric.

It has been found that actinide metal of such improved characteristics can be obtained if a specific electrolyte and relatively low temperatures are used for the electrolyzing step. To be more particular, the objects of this invention are accomplished by electrodepositing actinide metal from a fused bath having a temperature between 385 and 425 C. and consisting of from to 50% by weight of actinide halide and from 95 to 50% of the eutectic mixture of lithitun chloride and potassium chloride.

The lithium chloride-potassium chloride eutectic contains 45% of LiCl and 55% of KCl and has a melting point of 325 C. While from 5 to 50% of the actinide halide may be present in the electrolyte a quantity of from 20 to 35% has been found preferable.

The process of this invention may be utilized for the preparation of all actinide elements; it has been found particularly valuable, however, for the production of thorium and uranium. The tetrafluoride proved to be by far the preferred halide starting material; this is especially true for the production of uranium. However UCls, for instance, was also found satisfactory.

It is advisable, though not necessary, to carry out the process in an inert atmosphere; argon gas has been found suitable for this purpose.

A great number of materials which are not attacked by the substances present in the electrolyte and by any of the side products formed may be used for the anode, and the uranium tetrafluoride decomposed by the process is then replenished from time to time. In a particularly advantageous embodiment of the process of this invention, however, uranium is employed as the anode material; the uranium is dissolved from the anode as the uranium tetrafluoride in the bath is decomposed by the electrolysis. This entails an automatic regeneration of the uranium tetrafluoride and thus of the electrolyte thereby permitting Z,739,1 l l Patented Mar. 20, 1956 process can be combined with the uranium production.

process without the addition of any extra steps. p

The cathode is suitably made of tantalum or molybdenum, the latter being the preferred material. However, other suitable materials may also be used.

The electrolyte of this invention starts to melt at 385 C. and is completely melted at 400 C. An operation temperature of between 400 and 425 C. was found to represent optimal conditions, and these low temperatures proved primarily to be responsible for the high purity of the product and also for the large size of the crystals. A decrease of operating temperature brought about an increase of crystal size of the final product.

A voltage of from M4 to 15 volts and a current density of from 5 to amps/sq. drn. gave the best results, the lower current densities within that range yielding a slower deposition, of course, but larger-size crystals.

The metals obtained by the process of this invention were nearly always of spectroscopical purity. In the case of uranium production, using a uranium anode, the carbon content was reduced in one instance from 440 p. p. m. (in the anode material) to 1-2 p. p. m. (in the final product deposited at the cathode).

The uranium produced by this process usually contains relatively large quantities of lithium and potassium derived from the electrolyte. These alkali metals can be easily removed, though, by melting the uranium, e. g. in a crucible of uranium dioxide, whereby the. lithium and potassium are volatilized. I

In the following an example of the process of this invention is given for illustrative purposes only.

Example An electrolytic cell made of a heat-resistant glass contained a bath consisting of 70% by weight of the lithium chloride-potassium chloride eutectic and 30% of uranium tetrafiuoride. The anode consisted of uranium, while a molybdenum rod served as the cathode. Electrolysis was allowed to run over a three-month period at a current density of between 10 and 15 amps./sq. dm. and a bath temperature of between 400 and 425 C. Addition of uranium tetrafluoride was not necessary during this time. The metal deposited was in the form of coarse dendrites and crystals ranging from Ms to A" in length. These crystals were analyzed and found to contain:

Some twenty other elements were below the limits of spectrographic detection. After remelting forremoval of potassium and lithium the uranium was of 99.993% purity.

It will be understood that this invention is not to be limited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

l. A method of purifying a carbon-containing actinide metal selected from the group consisting of uranium and thorium, comprising passing electric current through a cathode, an anode of said metal and a fused bath consisting of from 5 to 50% by weight of the actinide tetrafluoride and from to 50% of the lithium chloridepotasiumm chloride eutectic, and having a temperature of; from 3135 to 425 C. whereby actinide metal of greatly 7 reduced carbon content is deposited on the cathode.

2. The method of claim 1 wherein the tetrafiuoride is uranium tetrafluoride.

3. Themethod ofclaim 1 wherein the tetrafluoride is thorium tetrafluoride.

'4. The method of claim 1 wherein the bath contains from 20 to 35% of the, actinide tetrafiuoride.

5. The method of claim 1 wherein electrodeposition is I is'carried 'out'at from /4, to 15 volts and from;5 to 7 5 amps/sq. dec.. 1 V

6. A method ct -purifying a carbon-containing ractinide metal selected from the. group consisting of uraniumand thorium, comprising passing electric current through a cathode, ananhdeiof said metal and a fused bathconsistinzof-frornS to 50% by weight of the actinide tetrafl'uoride andifrom 95 toz50% of the lithium chloride- 'p0tas;s,ium' chloride eutectic and having 'a temperature of from-385t0w425 C. whereby actinide metal-ofigreatly v reduced carbon content is c V y y 1 deposited on the cathode, and melting the actinide metal deposited at the'ca'thode whereby any lithium and potassium metals present are volatilized.

Ofiicial Gazette, vol. 657, page 1587, of the Ofiicial Gazette. 

1. A METHOD OF PURIFYING A CARBON-CONTAINING ACTINIDE METAL SELECTED FROM THE GROUP CONSISTING OF URANIUM AND THORINUM, COMPRISING PASSING ELECTRIC CURRENT THROUGH A CATHODE, AN ANODE OF SAID METAL AND A FUSED BATH CONSISTING OF FROM 5 TO 50% BY WEIGHT OF THE ACTINIDE TETRAFLUORIDE AND FROM 95 TO 50% OF THE LITHIUM CHLORIDEPOTASIUMM CHLORIDE EUTECTIC, AND HAVING A TEMPERATURE OF FROM 385 TO 425* C. WHEREBY ACTINIDE METAL OF GREATLY REDUCED CARBON CONTENT IS DEPOSITED ON THE CATHODE. 